1. Field of Invention
The present invention relates to a projection lens, and more particularly to a zooming lens with low cost.
2. Description of the Prior Art
Recently, bulky Cathode Ray Tube (CRT) projectors have been gradually replaced by Liquid Crystal Display (LCD) or Digital Light Processing (DLP) projectors. An advantage of LCD or DLP projectors is the compact size and portability. Another advantage is that they can be directly hooked up with digital appliances to display the projected images. With such advantages, the LCD and DLP projectors are taking broader market. To enhance the competitiveness in the market, the manufactures are striving to reduce the production cost and retail price.
Generally, a projection device produces images by means of an optical engine, where an image is generated, and then by a zooming lens, whereby the images are projected onto a screen. Consequently, the cost of a projection device mainly depends on the optical engine and zooming lens.
FIG. 1A and FIG. 1B schematically illustrate the structure of a conventional zooming lens. Referring to FIGS. 1A and 1B, a conventional zooming lens 100a comprises three sets of lenses, 110a, 120a and 130a respectively composed of four lenses 112, two lenses 122 and four lenses 132.
As above-described, as the zooming lens 100a zooms in from its tele-end (as shown in FIG. 1A) to wide-end (as shown in FIG. 1B) by adjusting the magnification, or conversely, zoom out from its wide-end to tele-end, these three sets of lenses 110a, 120a and 130a have to move simultaneously for magnified or reduced effect. To achieve such purpose, an interlock mechanism among the set of lenses 110a, 120a and 130a must be employed in the zooming lens 100a. In turn, the production cost is increased with the complexity of the mechanism structure.
FIG. 2A and FIG. 2B schematically illustrate another conventional zooming lens. Referring to FIGS. 2A and 2B, the conventional zooming lens 100b mainly comprises two sets of lenses, 110b and 120b, which are respectively composed of six lenses 112 and four lenses 122.
As described above, when the magnification of the zooming lens 100b changes from its tele-end, as shown in FIG. 2A, to the wide-end, as shown in FIG. 2B, or changes from its wide-end to the tele-end, these two sets of lenses 110b and 120b move simultaneously for achieving the effect of magnifying or reducing the magnification. Since this zooming lens 100b only need to cause the two sets of lenses to simultaneously move together when changing the magnification, therefore it has a simpler mechanical design, resulting in lower fabrication cost.
Since the lenses are manually assembled, the addition one of the lens causes the increase of fabrication cost for the lens itself, but also the increase of number of elements and assembling time in manpower. As a result, although the zooming lens 100b is cheaper than the zooming lens 100a, it still has a higher production cost because of the zooming lens 100b still needs ten pieces of lenses, causing the still increase of fabrication cost.